A surface plasmon refers to a fluctuation in the electron density, i.e., a collective vibration of an electron gas (or plasma) at the boundary surface of two materials of which real number terms of complex dielectric constants have opposite signs to each other. In this case, a surface plasmon wave generated by the surface plasmon is a surface electromagnetic wave propagating along the boundary surface between the two materials, i.e., a metal and a dielectric medium. The surface plasmon exists at the boundary surface between the metal having a negative (−) polarity and the dielectric medium and is excited by electrons or photons accelerated at high speed.
The surface plasmon is a transverse-magnetic (TM) polarized wave and the magnitude of an electric field or a magnetic field forming the wave is decreased exponentially as it goes far away from the metal while being the largest on the metallic surface. Owing to this characteristic, the surface plasmon has widely been used for measurement of the property of the material existing on the metallic surface and the optical constant of the metal itself.
Also, the surface plasmon has lots of merits in its application to a sensor or the like because the electric or magnetic field is concentrated at the proximity of the metal, and is applied as an optical device due to its susceptible response to perturbation of the metallic surface.
Korean Patent Laid-Open Publication No. 2002-15617 proposes a sensor that senses rare earth elements using a surface plasmon resonance. The Korean patent teaches that the sensor is constructed such that a nickel-chromium thin film and a gold thin film are coated on a glass substrate and then a sensing film is coated on the top surface of the thin film layer so as to selectively analyze rare earth elements.
Korean Patent Laid-Open Publication No. 2004-102847 discloses an analysis device that measures the interaction of a biochemical material and a biological material using a surface plasmon resonance phenomenon. The Korean patent teaches that the analysis device can modify the shape of a prism which generates a surface plasmon effect to thereby extend the limitation of measurement.
Korean Patent Laid-Open Publication No. 2004-39553 proposes an immunosensor using a localized surface plasmon phenomenon. The Korean patent teaches that a plurality of nanometer-level metallic structures is formed to be in contact with a specimen on a substrate to thereby further increase sensitivity.
However, the aforementioned patents disclose a structure for generating the surface plasmon in which a metal is formed into a single thin film on a substrate. Such a structure has a disadvantage in that since it allows the surface plasmon to be formed only on the surface of the metallic thin film, the surface plasmon propagates within a very short distance.